The United Kingdom has informed European Council President Donald Tusk's office of May's intention, May's spokesman said, confirming an earlier Reuters report from Brussels.

"Last June, the people of the UK made the historic decision to leave the EU. Next Wednesday, the Government will deliver on that decision and formally start the process by triggering Article 50," Brexit minister David Davis said in a statement.

The move will begin a two-year negotiating period in which the British government and the EU hope to agree on the terms of Britain's exit and reach a separate deal on the shape of their future relationship, most importantly on the terms of trade between the two.

"We are on the threshold of the most important negotiation for this country for a generation," Davis said.

"The Government is clear in its aims: a deal that works for every nation and region of the UK and indeed for all of Europe – a new, positive partnership between the UK and our friends and allies in the European Union."